Saturday, March 24, 2012

Analysis of RadioShack Duster Spray

In research and industry, spraying with compressed gas (usually dry nitrogen) is the standard way to remove liquid from a specimen after solvent cleaning or rinsing. By blowing the liquid off rather than letting it evaporate, spots from dissolved contamination are reduced or eliminated.

I had been using RadioShack duster spray for a while but started noticing residue on samples dried with it. My hypotheses at this point were:

The solvent had contamination in it, either from cleaning the sample or a contaminant in my stock bottle, and was depositing the contaminant on my samples

The bitterant added to the duster spray (to deter people from using it as an inhalant) was less volatile than the gas (or not volatile at all) and leaving residue on the samples

Earlier today I decided to test the spray and see if I could find out whether it was the source of the contaminant. Since the labeling on the can indicated pretty clearly that breathing it wasn't a great idea, all of my work was done in the fume hood.

The subject of today's experiments

I began by inverting the can and spraying a liquefied sample of the duster (R-134A refrigerant, according to the label on the can) into a test tube. The tube was quickly coated in frost as the refrigerant evaporated.

Frost-covered test tube

After trying to place some of the liquid onto a microscope slide with little success (it boiled as soon as the pipette touched it) I ended up pouring it into a petri dish and leaving it on the hot plate to evaporate all of the refrigerant and condensed water.

R-134a and condensed water slush being evaporated on the hot plate

Non-volatile contamination deposited on petri dish

Non-volatile contamination deposited on microscope slide

The results were pretty conclusive - some non-volatile contaminant is definitely present in the spray. I'm not sure what it is, and see little point in trying to identify it, but I clearly need to find a new source of duster gas for my experiments.

I'm looking at CleanTex duster spray, from the vendors of Texwipe cleanroom wipers. According to the specs on the website it's particulate filtered down to 200nm and is pure compressed gas with no bitterant or other stuff added.

I'm not really concerned about cost as I use such a small volume of gas. Much better to go for high quality.

The main alternative I was considering, actually, was compressed nitrogen like the real shops use. The problem is that it's hard to get in small volumes, I'd probably have to buy a giant 56l cylinder (http://www.sigmaaldrich.com/catalog/product/aldrich/295574?lang=en&region=US) or something along those lines. That would be expensive as well as posing the safety/handling associated with large cylinders of inert gas under pressure.

Probably going to go with the CleanTex spray, at the rate I go through it one or two cans should last me months.